let str = "Hello";  //String  '[1,2,3]'
//console.log(str.charAt());
//console.log(str.length);
//console.log(str[0]);

let num = 123;  //Number
console.log(num);
console.log(num.toString());

let flag = true;  //Boolean
console.log(flag);

let un =undefined

let nu =null;

// 以上都是字面量

//以下都是构造函数的创建方式
let str2 =new String("Hello");
//console.log(str2);
let num2 =new Number(123);
let flag2 =new Boolean(true);

//let un2 = new Undefined(); //x 没有这个方法
//let nu2 = new null()      //x 没有这个方法


let s1 ='Hello';
let s2 ='Hello';
console.log(s1===s2); //true
let sy1 =Symbol("Hello");
let sy2 =Symbol("Hello");
console.log(sy1===sy2); //false   每个Symbol都是独一无二的